<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>表格合并</title>
</head>
<body>
    <table border="1px" cellpadding="0" cellspacing="0" width="400px">
        <tr>
            <td colspan="3" style="background-color: aqua">a</td>
        </tr>
        <tr>
            <td>4</td>
            <td>5</td>
            <td>6</td>
        </tr>
        <tr>
            <td>7</td>
            <td>8</td>
            <td>9</td>
        </tr>
    </table>
</body>
</html>